$\dfrac{15}{100} + \dfrac{4}{10} = {?}$
Explanation: The fractions must have the same denominator before you can add them. Rewrite $\dfrac{4}{10}$ as $\dfrac{40}{100}$ $\dfrac{15}{100} + \dfrac{40}{100} = {?}$ $ = \dfrac{55}{100}$